The invention relates to a camshaft adjuster for an internal combustion engine comprising a vane wheel which is firmly mounted on a camshaft for rotation therewith and rotatably supported in a drive component in which the vanes extending from a base cylinder into partial annular chambers formed by radially inwardly extending wall members of the drive component so that, in circumferential direction at opposite sides of each vane, a pressure chamber is formed to which pressurized oil can be admitted for adjusting the angular position of the vane wheel relative to the drive component.
Camshaft adjusters are used in connection with valve controlled internal combustion engines in order to change the angular position of the camshaft relative to the crankshaft of the engine. In this way, the opening and closing times of the gas exchange valves relative to the top dead center position of a piston can be advanced or retarded so as to optimize the charge change of the combustion chamber or, respectively, the cylinders depending on the respective operating point of the internal combustion engine.
DE 196 23 818 A1 discloses a camshaft adjuster which includes a vane wheel. The vane wheel is mounted on the camshaft for rotation therewith and supported in a drive component so as to be rotatable relative thereto over a limited range. The drive component is driven by the crankshaft of the internal combustion engine generally by means of a toothed belt. The vanes of the vane wheel extend into spaces in the drive component which are formed between radially inwardly extending projections of the drive component. The projections delimit a maximum angular range within which the vane wheel is rotatable relative to the drive component. Between the vanes and the projections hydraulic pressure chambers are formed which are controlled by a control valve, by which pressurized oil is supplied to, or released from, the hydraulic pressure chambers so that the position of the vane wheel relative to the drive component is obtained by the pressure conditions in the pressure chambers disposed at circumferentially opposite sides of the vanes. When the engine is not operating the vane wheel is moved by springs to one of its end positions in the drive component and locked therein by a locking bolt which is axially slidably supported either in the vane wheel or in the drive component and extends into a locking bore in the drive component or, respectively, the vane wheel. In the locked end position of the vane wheel the camshaft must be in an angular position relative to the crankshaft in which the internal combustion engine can be easily started. After engine startup, the angular position of the vane wheel relative to the crankshaft is controlled in accordance with a performance graph of the internal combustion engine. Since the locked end position of the vane wheel limits the advancing or retarding adjustment of the camshaft, the timing of the gas exchange valves cannot be advanced or retarded beyond this end position during operation of the engine.
The vane wheel must be locked during the startup phase in order to prevent undesired movements of the vane wheel and the camshaft, by oscillations for example, during the startup phase in which the vane wheel cannot yet be stabilized by an adequate operating pressure. As soon as a sufficient operating pressure has developed in one of the chambers so that the position of the vane wheel in the drive component can be stabilized, the locking bolt is moved by the operating pressure out of the locking bore and remains in such a release position as long as a sufficient operating pressure is present in the chamber.
Camshaft adjusters are also suitable for changing the relative angular positions of two camshafts of which one actuates the inlet valves and the other actuates the outlet valves.
It is the object of the present invention to optimize the operation of an internal combustion engine by optimizing the adjustment range for the relative angular positions of the vane wheel, that is, the camshaft and the drive component.